1. Field of the Invention
The present invention relates to a motor drive apparatus in which a main power supply used for motor drive is supplied via a magnetic contactor.
2. Description of the Related Art
In a motor drive apparatus for driving a motor in machine tools, a forging press machine, an injection molding machine, an industrial machine, or various types of robots, a main power supply used for driving the motor is supplied from an AC power supply side via a magnetic contactor. When driving the motor, the motor drive apparatus is powered on by contacts of the magnetic contactor being closed (on). In this manner, an AC power serving as main power supply is supplied to the motor drive apparatus from the AC power supply side via the magnetic contactor, and the motor drive apparatus converts the AC power to power suitable for driving the motor and supplies the power to the motor.
Generally, the magnitude of the main power supply voltage (e.g., the rated voltage) which is allowed for the motor drive apparatus is set beforehand depending on various factors such as the type and use of the motor to be driven or the performance and structure of the motor drive apparatus. However, when an inappropriate AC power supply in excess of the rating is erroneously connected to the motor drive apparatus, a voltage of a value exceeding the allowable main power supply voltage is applied to the motor drive apparatus, thus sometimes causing a damage to the components constituting the motor drive apparatus and/or the motor per se.
For example, as described in Japanese Unexamined Patent Publication (Kokai) No. 2010-226893, there is a power supply device configured to prevent a damage to or deterioration of a component or load due to application of an overvoltage even when a wrong power supply is connected, wherein while a predetermined time is counted from when an opening and closing circuit is closed, a charged voltage is monitored across a smoothing capacitor for smoothing a DC voltage rectified from an AC power supply by a rectifier circuit, and when the charged voltage exceeds a predetermined voltage, the opening and closing circuit is opened.
Further, for example, as described in Japanese Unexamined Patent Publication (Kokai) No. 2003-061384, there is a motor drive apparatus in which switch control means for controlling the operation of a switch element of an inverter in the motor drive apparatus is equipped with an overvoltage protection function, and it is configured such that when a voltage in excess of the rating is applied to the switch element, the protection function works to shut off a gate voltage, thereby preventing a damage to the switch element.
As described above, when an AC power supply which is excessive for the rating of the motor drive apparatus is erroneously connected, a voltage having a value which is greater than the allowable main power supply voltage is applied to the motor drive apparatus, thus sometimes causing a damage to the components of the motor drive apparatus and/or the motor per se.